Catalyst components for the stereospecific polymerization of olefins are widely known in the art. Concerning the polymerization of propylene, the most spread out catalyst family belongs to the Ziegler-Natta category and in general terms it comprises a solid catalyst component, constituted by a magnesium dihalide on which are supported a titanium compound and an internal electron donor compound, used in combination with an Al-alkyl compound. Conventionally however, when a higher crystallinity of the polymer is required, also an external donor (for example an alkoxysilane) is needed in order to obtain higher isotacticity. One of the preferred classes of internal donors is constituted by the esters of phthalic acid, diisobutylphthalate being the most used. The phthalates are used as internal donors in combination with alkylalkoxysilanes as external donor. This catalyst system gives good performances in terms of activity, isotacticity and xylene insolubility. One of the problems associated with the use of this catalyst system is that the phthalates have recently raised concerns due to the medical issues associated with their use and some compounds within this class have been classified as source of heavy health problems. Consequently, research activities have been devoted to discover alternative classes of internal donors for use in the preparation of catalyst components for propylene polymerization. U.S. Pat. No. 7,388,061 discloses diesters belonging to the formula R1—CO—O—CR3R4-A-CR5R6—O—CO—R2 in which R1 and R2 groups, which may be identical or different, can be substituted or unsubstituted hydrocarbyl having 1 to 20 carbon atoms, R3—R6 groups, which may be identical or different, can be selected from the group consisting of hydrogen, halogen or substituted or unsubstituted hydrocarbyl having 1 to 20 carbon atoms, R1—R6 groups optionally contain one or more hetero-atoms replacing carbon, hydrogen atom or the both, said hetero-atom is selected from the group consisting of nitrogen, oxygen, sulfur, silicon, phosphorus and halogen atom, two or more of R3—R6 groups can be linked to form saturated or unsaturated monocyclic or polycyclic ring; A is a single bond or bivalent linking group with chain length between two free radicals being 1-10 atoms, wherein said bivalent linking group is selected from the group consisting of aliphatic, alicyclic and aromatic bivalent radicals, and can carry C1-C20 linear or branched substituents; one or more of carbon atoms and/or hydrogen atoms on above-mentioned bivalent linking group and substituents can be replaced by a hetero-atom selected from the group consisting of nitrogen, oxygen, sulfur, silicon, phosphorus, and halogen atom, and two or more said substituents on the linking group as well as above-mentioned R3—R6 groups can be linked to form saturated or unsaturated monocyclic or polycyclic ring. The very broad definition of the A group encompasses a huge number of diol skeletons from which corresponding diesters can be generated. However, when the bridging group A includes an aromatic structure (like phenyl or diphenyl as in examples 4, 17, 62, 79-80) the balance activity/stereospecificity is greatly unsatisfactory and in fact the same ester groups perform much better when associated to diols skeleton based on aliphatic structure.